Everyone loves a nice sunny day at the beach, soaking up the rays, relaxing, or swimming. This idyllic scene is the epitome of serenity, peace, and fun. While the views are lovely and the sun offers numerous health benefits, we must also be aware of the potential risks associated with prolonged sun exposure. 

One significant risk is melanoma, a type of skin cancer often linked to increased sun exposure, which exists in multiple forms. The more well-known form, cutaneous melanoma, has a strong link to sun exposure and is commonly diagnosed.²

However, there is also a rarer type called mucosal melanoma, which is less well-known and not linked to sun exposure. By exploring the differences and similarities between these two forms of melanoma, we can enhance our understanding and make more informed decisions about our health.

The Hidden Dangers of Sun Exposure

Melanoma is the deadliest form of skin cancer, and its incidence rate is currently on the rise, with an increase of 320% from 1975 to 2018. Melanoma is responsible for approximately 90% of skin cancer deaths, despite constituting only a small fraction of total skin cancer cases. This high death rate is likely due to its significant metastatic potential and resistance to conventional therapies, which make it difficult to treat, especially if not diagnosed early. 

Given the substantial clinical challenges melanoma presents, raising awareness is crucial for early detection and prevention.

What is melanoma?

Melanoma originates from melanocytes, a type of cell predominantly found in the skin and eyes that produces the pigment melanin, which gives our skin and eyes their colour.^1,2 

Melanoma begins when an aberration occurs in melanocytes, damaging DNA and causing the cells to grow uncontrollably. The exact causes of melanoma are not fully understood, but there are several known factors, depending on the type, that can increase the risk.

Cutaneous Melanoma

Cutaneous melanoma is the most common form of melanoma, typically developing on areas of skin that are sun-exposed but can also occur in areas not regularly exposed to sunlight. Cutaneous melanoma can be life-threatening if not detected and treated early; however, the severity depends on various factors, including the thickness and depth of the tumour and whether it has spread to other parts of the body. 

The symptoms of cutaneous melanoma can vary depending on the individual and its origin, but the most common symptoms are known as the ABCDEs of melanoma.

ABCDE’s of Cutaneous Melanoma:

• Asymmetrical moles- Melanoma often appears as a mole or skin growth that is asymmetrical, meaning one half does not match the other half
• Borders that are irregular – Melanoma sores often present with irregular borders or edges that are not smooth
• Colours that change –  A single melanoma lesion can exhibit multiple colours, including shades of black, brown, blue, red, or white
• Diameter of 6mm or more – Melanoma lesions usually have a diameter larger than 6mm but can be smaller
• Evolving appearance – Melanoma moles often change in size, shape, and colour

Who Can Get Cutaneous Melanoma?

Individuals of all ages and ethnicities can develop cutaneous melanoma; however, some individuals are at greater risk.

One of the most significant risk factors is prolonged exposure to ultraviolet (UV) radiation from tanning beds or direct sunlight. Exposure to UV radiation can damage DNA, leading to mutations that result in cancer.

Other risk factors include having fair skin. This is because individuals with fair skin produce less melanin, which acts as a protectant against the harmful effects of UV radiation. Melanin can absorb and dissipate UV rays, reducing the risk of DNA damage. Therefore, those with lower levels of melanin are more vulnerable to UV radiation damage. 

Furthermore, repeated sunburns increase the likelihood of DNA damage and the subsequent development of skin cancer. Fair-skinned individuals are at a higher risk of sunburn and therefore have a greater chance of incurring DNA damage that could result in melanoma.^2,3

Additionally, other factors that contribute to the development of cutaneous melanoma include:

• Weakened immune system
• Age – The risk of cutaneous melanoma increases in individuals over the age of 50 
• Family History – Having a close relative with a history of melanoma increases the chance of developing it. Certain genetic mutations are also believed to contribute to familial melanoma

90% of cutaneous melanoma cases are believed to be due to UV radiation from the sun or indoor tanning devices. This can often be identified by measuring the type and amount of DNA damage in the melanoma tumour sample.

How Is Cutaneous Melanoma Treated?

The treatment of cutaneous melanoma varies between patients, depending on the stage of the cancer, tumour size and location, and the individual’s overall health. The main treatment options include:

• Surgery – Surgery is the primary option for localised melanoma. The aim is to remove the tumour with minimal healthy tissue removed
• Immunotherapy – This utilises medication that stimulates the immune system to recognise and attack cancer cells 
• Targeted Therapy – This form of therapy uses drugs that target specific genomic mutations or proteins within melanoma cells

Many of the symptoms, causes, and treatments for cutaneous melanoma are similar to those for other types of melanoma, but there are some differences.

Mucosal Melanoma

Mucosal melanoma is a less well-known type of melanoma, partly because it is a rare form, accounting for approximately 1% of all melanoma cases.  Compared to cutaneous melanoma, mucosal melanoma is generally more aggressive and typically has a poorer prognosis due to late diagnosis. 

While cutaneous melanoma usually develops on skin cells, mucosal melanoma originates in the mucosal membranes of the body, such as those lining the nose, mouth, throat, anus, or genital areas. 

Research has identified that around half of mucosal melanoma cases begin in the head and neck areas (i.e., mouth, nose, large airways, oesophagus), with the remaining occurring in the lower large intestine, urinary tract, and reproductive organs. 

Due to these different areas of development, the symptoms of mucosal melanoma differ from those of cutaneous melanoma.

Symptoms of Mucosal Melanoma:

• A lump or growth in the affected area
• Discomfort or pain in the affected area
• Bleeding or other discharge from the affected area
• Haemorrhoids (swollen veins in the region of the anus) that do not heal
• Difficulty swallowing or breathing (if the melanoma has developed in the throat)

Unlike cutaneous melanoma and other types of melanoma, sun exposure is not a risk factor associated with mucosal melanoma. Similar to cutaneous melanoma, age and family history are risk factors; however, some risk factors unique to mucosal melanoma include:

• Gender – Women are more likely to develop mucosal melanoma than men; the exact reasoning is not fully understood, but it is believed to be related to anatomical and hormonal factors
• Race – Unlike cutaneous melanoma, mucosal melanoma is more common in individuals with darker skin tones. This is believed to be due to genetic factors, lower awareness about the risk, and later diagnosis
• Exposure to particular chemicals - e.g., those used in the textiles industry

The main challenge with mucosal melanoma is its difficult to treat. Treatment for localised mucosal melanoma that has not spread includes surgery, often followed by radiation therapy^. However, mucosal melanoma is often diagnosed quite late, particularly in comparison to cutaneous melanoma. Advanced stages of mucosal melanoma involve metastatic disease, where the melanoma has spread. 

At this stage, the melanoma is unresectable, meaning it cannot be removed with surgery, and the primary treatment is often radiation therapy. 

Unfortunately, mucosal melanoma does not respond well to approved immunotherapies compared to cutaneous melanoma. 

Additionally, radiation therapy is not suitable for all patients, especially those with compromised immune systems. To address this, clinical trials are underway to develop therapies specifically for patients with mucosal melanoma.

Summary

Cutaneous and mucosal melanoma are both potentially life-threatening forms of melanoma, each with distinct causes, symptoms, treatments, and characteristics.^1,2,3

Mucosal melanoma is typically more aggressive than cutaneous melanoma, partly due to later diagnosis resulting from a lack of awareness of its symptoms. While the symptoms of cutaneous melanoma often involve visible abnormalities on the skin, the symptoms of mucosal melanoma mainly cause abnormalities and discomfort in internal body linings and tissues. 

The main cause of cutaneous melanoma is believed to be prolonged sun exposure. In comparison, the causes of mucosal melanoma are less well-understood, highlighting the need for more research in this area. 

Understanding the distinctions between cutaneous and mucosal melanoma not only deepens our knowledge of these conditions but also promotes better health through earlier diagnoses and targeted treatments.